The present invention relates to a golf club head provided with a vibration absorber capable of absorbing unpleasant vibrations on off-center hits, without absorbing agreeable vibrations on on-center hits.
In the Japanese Patent Application Publication No. 2006-129936A, there is disclosed an iron-type golf club head composed of a face member and a main body between which a shock absorber made of an elastic material is disposed in order to improve the impact feeling.
In the U.S. Patent Application Publication NO. 2007-129165-A1, there is disclosed a golf club head provided with a vibration absorber in order to absorb vibration of a golf club head at impact, wherein the absorber is made of a first visco-elastic material and a second visco-elastic material whose loss coefficient (loss tangent) has a different temperature dependency than that of the first visco-elastic material so as to cover a wide frequency range of the vibrations.
On the other hand, it is empirically well known to the golfers that, in the case of good shots such that the ball is hit at the sweet spot of the club face (namely, on-center hit), the player feels solid agreeable vibration at the hands through the grip, but in the case of miss shots such that the ball is hit off the sweet spot (namely, off-center hit), the player feels dull unpleasant vibration and sometimes numbness at the hands.
Thus, the vibration include the agreeable vibrations on on-center hits, and the unpleasant vibrations on off-center hits.
From various test results, it was confirmed that the vibrations on on-center hits are higher in the frequency and smaller in the amplitude than the vibrations on off-center hits.
Therefore, if a plurality of visco-elastic materials different in the loss coefficient are used in one golf club head in order to absolve vibrations of a wide frequency range, then not only the unpleasant vibrations on off-center hits but also the agreeable vibrations on on-center hits are absorbed. Therefore, the impact feeling is blurred and considered as being not good for advanced golfers in particular, and as a result, the golf club head is felt by the player as being difficult to control the ball.
The present inventor studied and discovered that, if a visco-elastic material is provided with a narrow cut, then by changing the direction of the cut, the vibration absorbing power is also changed, and it is possible to discriminate the relatively low frequency, relatively large amplitude vibration on miss shots from the relatively high frequency, relatively small amplitude vibration on good shots.
It is therefore, an object of the present invention to provide a golf club head, in which, by providing a vibration absorber with a narrow cut, unpleasant vibrations on miss shots are effectively absorbed while keeping pleasant vibrations on good shots as much as possible, and thereby the impact feeling is prevented from becoming blurred so that the head can provide good impact feeling.
According to the present invention, a golf club head comprises a head main body made of a metal material and having a club face for striking a ball, and a vibration absorber made of a viscoelastic material and attached to the head main body, wherein the vibration absorber is provided with a cut having a width of not more than 1.0 mm.
Preferably, the cut is substantially parallel with the club face, and the surface at which the cut is opened, comes into contact with the head main body.
Therefore, when the vibration on miss shots, which is a relatively low frequency, relatively large amplitude vibration is applied, the nearby portions on both sides of the cut are moved, changing the positive width therebetween or causing friction between the contacting surfaces in the case of zero width. As a result, the vibration energy is transformed into heat, and the vibration is absorbed or damped effectively.
On the contrary, when the vibration on good shots, which is a relatively high frequency, relatively small amplitude vibration is applied, the nearby portions on both sides of the cut are not so moved, thus the vibration energy is not so absorbed. As a result, the head can provide a good impact feeling on good shots and miss shots.
In the following description, the dimensions, positions and directions refer to those under the standard state of the club head unless otherwise noted. Here, the standard state of the club head 1 is such that the club head is set on a horizontal plane HP so that the axis CL of the club shaft(not shown) is inclined at the lie angle (alpha) while keeping the axis on a vertical plane, and the club face F forms its loft angle (beta) with respect to the horizontal plane HP. Incidentally, in the case of the club head alone, the center line of the shaft inserting hole 6a can be used instead of the axis of the club shaft.
“Sweet spot SS” is the point of intersection between the club face F and a straight line N drawn normally to the club face F passing the center of gravity G of the head.
“Back-and-forth direction” is a direction parallel with the straight line N projected on the horizontal plane HP.
“Heel-and-toe direction” is a direction perpendicular to the back-and-forth direction and parallel with the horizontal plane HP.
“Up-and-down direction” is a direction perpendicular to the horizontal plane HP.